Motor mounts.....I thought they were all the same???

[thefarmboy21]

I just dropped a 350 in my K20 last night and the clamshells on the block wouldn't slide over the mounts in the frame. So I took the lowers out because they were already loose.....I bolted them into the clamshells themselves and set it down......all the hold in the frame disappeared?!?! I thought GM used the same uppers and lowers on everything? The lowers are from the factory 6cyl (after I installed the V8 cross brace) and the uppers are just two of several sets I had laying around. So what'd I do wrong? Are there different clamshells or are the lowers different? Both top and bottom look the same as all the others I've ever seen. The bolt holes look to be off by 1/2" so you probably couldn't tell with the naked eye. Thanks!

[thefarmboy21]

I'm not getting the help here that I thought I would, but some google research shows some potential....I guess the chevy replacement frame pad, motor mount #'s 2292, 2621 and 2395 all look virtually identical but all change the positioning of the engine. SOO.....I'm hoping I can go in to Autozone and pull them all and find the one that looks like it's shortest. I also have a few different sets of block mounts (clamshells) but I seem to have the most common and shortest set on the motor already.

[Engineer]

The clamshells for the 454 are taller than the ones used on a small block.

I have never found any differences on the rubber frame mounts.

[Captkaos]

Uppers are different depending on the engine.  Lowered are the same.  SBC and BBC can use the same mount but it will sit differently in the truck.  I have done this on several 1/2T's.

[thefarmboy21]

Well I changed one clamshell that was a little long/wide/whatever and one frame mount and it's in and bolted up now. I would've changed both frame pads but one of the mounts had the rubber in upside down. The bolt holes aren't the same top and bottom, and the ears the mounts ride on were in backwards.....took me about 10 minutes to figure out what happened. SOOO.....when buying new mounts, make sure they're MADE correctly.